WI would be more effective a keeping piston temps down however, an oil spray bar would be nice because you could easily run out of water and not know it. Of course you can run out of oil too, but you'll find out very quickly.

If in-cylinder temps are lowered and heat spikes are avoided then surely piston temps will be much better with WI.

I have an old paper that came up with the counter-intuitive results that W.I. doesn't reduce EGTs or various other temps that we'd expect to be affected. However it did notice temp reductions on the outside of the combustion chamber (sensors on the cyl head) which *might* be similar to piston temps. Hard to imagine a rig with temp sensors on the pistons!